Silicon is use in IC fabrication,
Because when we doped the Si its SINGLE CRYSTAL STRUCTURE remains same, it adjust the doping in its single crystal structure.
So the main property of Si remains same after doping profile.

None of the Answers mentioned here is right.It because of the excellent properties of silicon di oxide Silicon has become popular.I am not listing the properties of silicon dioxide here as all of you are familiar with it.
One can read in brief about the fabrication process here http://www.eecs.berkeley.edu/~hu/Chenming-Hu_ch3.pdf